Calling a function does not cause replication of its symbols. That
would happen if it were a macro, or an inline function, but not a simple
global function, which r4k_wait_irqoff is supposed to be, since (at
least the last time I worked with it), it is only called indirectly by
having its address stored in the cpu_wait function pointer. Either your
compiler is doing something insane and replicating the function each
time its address is taken (!), or someone has added another __pastwait
symbol somewhere.
And you are correct that moving the symbol to another function risks
breaking the functionality. Even if the compiler didn't reorder things -
which you are correct to note that it might do - you would create a
window during which the kernel would mistakenly believe that the CPU was
in the interrupt-disabled wait state when in fact it had just fallen out
of the loop and serviced an interrupt. I don't think that would
necessarily be fatal, but it would at least be inefficient.
Regards,
Kevin K.
Wu Zhangjin wrote:
Hi,
there is a guy reported a compiling problem in linux-2.6.29:
[...]
CC arch/mips/kernel/cpu-probe.o
{standard input}: Assembler messages:
{standard input}:3939: Error: symbol `__pastwait' is already defined
make[1]: *** [arch/mips/kernel/cpu-probe.o] Error 1
make: *** [arch/mips/kernel] Error 2
Seems I met this problem before, perhaps here is the reason:
arch/mips/kernel/cpu-probe.c:
void r4k_wait_irqoff(void)
{
local_irq_disable();
if (!need_resched())
__asm__(" .set push \n"
" .set mips3 \n"
" wait \n"
" .set pop \n");
local_irq_enable();
__asm__(" .globl __pastwait \n"
"__pastwait: \n");
return;
}
there is a global symbol __pastwait defined at the end of
r4k_wait_irqoff, if r4k_wait_irqoff is called more than one time, the
__pastwait will be multi-defined. so, need to be fixed. does this fix
it?
arch/mips/kernel/cpu-probe.c:
void r4k_wait_irqoff(void)
{
local_irq_disable();
if (!need_resched())
__asm__(" .set push \n"
" .set mips3 \n"
" wait \n"
" .set pop \n");
local_irq_enable();
return;
}
/* a dumy funciton for marking the end of r4k_wait_irqoff */
void __pastwait(void)
{
;
}
but I am not sure the gcc compiler will tune the position of the
r4k_wait_irqoff and __pastwait or not, so seems not safe. perhaps we
should change something else instead.
perhaps we should tune the __pastwait solution directly, just spark it,
not look into it yet, seems __pastwait is only used here:
arch/mips/kernel/smtc.c:
smtc_send_ipi:
if (cpu_wait == r4k_wait_irqoff) {
tcrestart = read_tc_c0_tcrestart();
if (tcrestart >= (unsigned long)r4k_wait_irqoff
&& tcrestart < (unsigned long)__pastwait) {
write_tc_c0_tcrestart(__pastwait);
tcstatus &= ~TCSTATUS_IXMT;
write_tc_c0_tcstatus(tcstatus);
goto postdirect;
}
}
best wishes,
Wu Zhangjin
